STRUCTURE OF MONOLAYERS OF SHORT-CHAIN N-ALKANOIC ACIDS (CH3(CH2)NCOOH, N = 0-9) SPONTANEOUSLY ADSORBED FROM THE GAS-PHASE AT SILVER AS PROBED BY INFRARED REFLECTION SPECTROSCOPY

This paper presents the results of an infrared spectroscopic and wettability examination of monolayers formed by the spontaneous adsorption of short chain n-alkanoic acids (CH3(CH2)nCOOH, n = 0-9) from the gas phase onto Ag. The infrared spectral data, collected in an external reflection mode, indicate that the monolayers chemisorb as the corresponding salt and that the chains contain all-trans conformational sequences for n = 1-9. The chemisorption process is further exemplified by the formation of a carboxylate group that is symmetrically bound at Ag as either a bidentate or bridging ligand. The conformational insights are developed on the basis of an unusually prominent series of the methylene wagging progression. An in-depth analysis resulted in the complete assignment of the fundamental modes in the progression as well as a reassignment of the CC stretch in the region of this progression. Structural insights developed from the infrared spectral data and contact angle measurements are compared to analogous monolayers formed from dilute solution. This comparison points to the subtle, but important, role of solvent in influencing the structure of the monolayer.